Mechanical attachment for azimuth offset bombing



B. L. HAVENS May 27, 1952 MECHANICAL ATTACHMENT FOR AZIMUTH OFFSETBOMBING m. Gsm u lFiled oct' I mvENToR BYRUN I. HAVE NS ATToRN EY May27, 1952 B. HAVx-:Ns

MECHANICAL ATTACHMENT FOR AZIMUTH OFFSET BOMBING 2 SHEETS-SHEET 2 FiledOct.

mvEN'roR BrRoN L; HA vE/vs ATTORNEY Patented May 27, 1952 UNITED STATESTENT OFFICE MECHANICAL ATTACHMENT FOR AZIMUTH OFFSET BOMBING Byron L.Havens, New York, N. Y., assigner, by 'Y mesne assignments, to theUnited States ofV America as represented by the Secretary of the NavyThis invention deals with bombing from aircraftV and more particularlywith the bombing of stationary ground targets by the use of the offsetbombing technique. I

Aircraft bombing equipment has been devel-V oped (cf. the copendin-gapplication lof `Byron L. Havens et al., Serial No. 620,134, `ledOctober 3, 1945, now abandoned) adapted chiefly for the blindV bombingof surface vessels (or other targets) through use of search radar; i.e., radar capable of supplying continuously the necessary information asregards the range and azimuth of the selected target. With the radarsupplying this information and by supplying manually informationpertaining to the bombingaircrafts air-speed and altitude, theproperrrelease point is computed by the equipment and the aircraft isproperly guided until it arrives at the computed release point. At thispoint, the bomb-release mechanism is energized automatically and thebomb is dropped.

The present invention involves a mechanical attachment for use inconjunction with the above referred to equipment, which attachmentfunctions to permit azimuth offset bombing mainly for overlandapplications, and comprises essentially a triangular linkage adapted tobe driven by a suitable motor to supplythe continuously-changing angularazimuth offset. This angular offset, when continuously supplied to theequipment, permits the radar operator to track more easily an aimingpoint other than the target, from which a stronger radar echo may beobtained, while at the same time establishing a straight ground Vcoursetoward the target.

The radar bombing system of the type described in `the above-identifiedcopending application is based upon the proposition that if one of twomoving objects moves in such a manner that the true bearing of thesecond object as seen from the rst remains unchanged, the two objectswill arrive at the same point at the same time and are said to be on acollision. course. The system operates to indicate to the pilot of thebombing aircraft the proper azimuthal position of the tracking pointrelative to a stable reference (gyro) so that the pilot may y theaircraft in such a direction that the azimuth to the target does notchange. It is proposed in this invention to track by radar an aimingpoint Vother than the target and it is a primary object to provide meansfor automatically and continuously adjusting the mean azimuthal positionof the radar sector scan so that the pilot, by flying the aircraft tomaintain no change in azimuth of the Fig. 1 is adiagrammaticrepresentation ofthe v geometry of offset bombing; 3.

Fig. 2 is a schematic representation of. the azi# muth section of theradar bombing system in which the present invention'is to be used;

Fig. 3 is a schematic representation of the azimuth section of the radarbombingsystem employing the present invention; Fig. 4 is a diagrammaticrepresentation in plan of the present invention; and

Fig. 5 Yisan elevational .view incrosssection of the construction shownin Figi.Y Y In order that the present invention and man@ ner in which itis utilized may be more fully understood there is illustrated inFig. 2 aschematic representation of the azimuth section .of' the radar bombingsystem of the above-cited copending application. It will be noted thatthis System employs a platform lrand a telescope bomb sight I4 bothstabilized in azimuth throughthe shaft l5 by means of the gyroscopeindicated on the diagram at Il. Provision is made by means of thedifferential gearing I2 and the target selection knob I3 ,for alteringthe bearing of the telescope |15 relative tothe gym-stabilized azi'-muth indicated by platform Ill.' As will be noted the azimuth pointingof the telescope I determines the cross hair bearing, which by limiteddefinition is taken to mean the particular azimuth bearing at which theradar beam must .be trainedrinorder that the Yazimuthal position. of thebeam of the cathode ray'tube may coincide with the stable azimuthvindicatedvon its face. This stable azimuth may,'for example, comprise avertical line etched on the face ofthe screen and may be called theazimuthcross hair.`.

As shown in the drawing, the l telescope I Vand the antenna i6 areinterconnected through a'suitable synchro-device l1 referredto in thedraw-'1 ing as a selsyn system, which interconnection' operates so thatany angular change inthe fcross hair bearing of the telescope t4introduced, for,

example, by means of the knob I3 and diii'erential I2 will produce alike change in the mean azimuthor bearing of the antenna I6. A motor I8is mechanically connected to antenna I6 andA is adapted to rotate theantenna at a constant angular velocity in azimuth. This motor is shownconnected electrically into the selsyn system and is provided for thepurpose of causing the antenna I6 to scan a sector about a referencedirection, i. e., the direction of the cross hair bearing. The detailsof the selsyn system and the circuit for producing the motor energizingvoltage, effective to produce the desired scanning action, are fullydescribed inthe copending application of John J. Lentz, Serial No.616,379, filed September 14, 1945; and, since these details areunnecessary to an understanding of vthis invention they are not repeatedhere.

The azimuth scanning circuit, which is indicated generally at I1, alsoprovides an azimuth sweep potential to the cathode ray tube Ireferr'ed'to hereafter as the B-scope. This 'feature of the system isillustrated diagrammatically in Fig. 2 by the two deecting plates 20 and2l shown connected electrically to the scanning circuit incorporated inthe selsyn system. In this manner the circuit shown in block at I1controls thesector scan as well as the azimuth deflection of theelectron beam of the B-scope. The nature of vthe 'scanning circuitincorporated in the synchro-deviceis such that whenthe radar beam ispointed in the direction determined by the shaft I5 and the telescopeI4, there is zero azimuth deflection on the B-scope; i. e., the beam ofthe B-scope is in the center'of the screen on the azimuth cross hair.The sector scan is approximately centered on the "cross hair bearing;thus as an aid in visualizing the operation of the system it may beconsidered that when the knob I3 is turned the Vtelescope and themeanaxis of the scan are Vturned together so as to illuminate the target.The more accurate statement, however, is that the pointing of thetelescope I4 corresponds to the cross hair'bearing instead of the meanaxis of scan, since the latter two may not exactly correspond.

`In the drawing, Figs. 2 and 3, the return signals or echoes from thetransmitting antenna are fed into the radar system indicated'in blockdiagram 22 and are shown applied to the intensity grid 23 of theB-scope, so that the signals returned from a target located within thesearch sector Will be portrayed as a bright spot on the screen, of theB-scope I9. The sector scan may be selected by altering the azimuthalposition of the telescope I4 and the antenna I5 until the desired targetor tracking kpoint appears in the center of the screen of the B-scope onthe azimuth cross hair. More complete details pertaining to the radarsystem disclosed herein by the block diagram 22, including theelectrical generation of the tracking vpip coincident with thetargetechoand the generation of a calculated'release-.pin maybe had byreference to the copending application SerialNo. 620,134. 1;

Referring now'to Fig. 1 of the drawing, there is shown the azimuthoffset geometry. It will be seen that with this system the approach tothe target line P-T will be a straight ground Atrack toward the target.If the bombing plane P moves from its presentposition P to a newposition along the path'P-T, thetrue bearing of the target 0T does notchange; however,l the bearing oftheaiming .or tracking point 0A NPA)does change continuously.

Vv"fortravel" in the slot 4Q 4of `the link 28.

It is an object in the bombing system herein discussed to present anazimuth indication of the aiming point on the radar screen to apply anoffset angle to the train of the radar antenna whereby the bombingaircraft may be maneuvered so that this aiming point indication will notdrift in azimuth and the bombing aircraft will follow a straight lineapproach to the target as indicated by the line P-T. With the radardirected toward the point A, selected because it is capable of producinga good radar echo, this point appears as a bright spot on the radarscreen. To maintain this point on the azimuth cross hair, and for'thebombing plane to follow a straight line course to the target, it isnecessary continuously to adjust the train of the radar antenna I6 sothat its center of scan will differ from the bearing of the target by anamount equal to the offset angle 0m.

As observed from Fig. l that as the bombing plane progresses -along the'P-T, there -will be at each instant a ytheoretically correct bearingfor point A, indicated on the rdrawing as QA. Since 0T is constant thevariable yportion Aoff-.'iA-is the offset angle Goff. Thepresentinvention comprises means for continuously adjusting the crosshair bearing for point A that vinvolves the generating of an angle equalto vor: and the adding of this angle to the azimuth ystabilized bearingof the telescope Ill, for example. With this angle added to the bearingof the line ofsight to the target (PT) the mean axis `o'f scan of theradar antenna (PA) will be such thatp'oint A will be observedfon theradar screen lalongthe azimuth cross hair. If the bombing plane followsa course indicated by P-T this representation of point A on the radarscreen will not move in azimuth; however, should-it appear to drift offthe azimuth cross hair the headingof the plane is Ychanged until thedesired conditionsare again maintained.

Referring now to Fig. 3 in the drawing, there is shown diagrammaticallya method for apply-v ing this offset angle to the radar bombing systemillustrated in Fig. 2. 25 has been added, including input and 'outputshafts indicated diagrammatically bythe lines 2li-24 respectively. Thisblock 25 and corresponding input and output shafts represent theYapparatus shown in detail in Figs. 4 'and f5.

This apparatus comprises Aapantograph formed of'a frame 33 and links 26,21 and 28. Link26 is driven by shaft 24, which shaft `is in turn drivenby shaft I5 lof Fig. 2. Accordingly the angular position of the links`26 and 28 corresponds tothe angle@T of Fig. 1 andrepresent the truebearing of the target. rThe .link v8 is 'rotatably supported on theshaft *243 which shaftserves as a means for transmitting the output ofthe pantograph linkage apparatus'to the antenna through'the selsynsystem `I1 by' being secured for rotation with the link '29, which linkmust therefore 'form an angle with the link 28 equal to the angle 00u.Accordingly, the position lof the link 29 corresponds withthe line .'PAof second pantograph or parallelogram with thev links 29, .34 land 35.The long arm 36 of the bell crank 3| .is slotted at 33'to receive the`sliding block 31, which block is also secured by meansof a pin 38'to'aslide (notshown) 'thatpis positioned Theblock It is noted that thelblock sitionable within'the slot 39 by rotation of the A sshown moreclearly in Fig. a pair of concentricdiscs 42 and 43 are mounted forrotation aboutthe output shaft 24. The outermost disc 43 is shownprovided with a pair of radial graduations `about its inner and outercircumference whereas the inner disc 42 is provided with an index mark44 adapted for cooperation with the innermost set of graduations. Thereis also pivoted about the shaft.24' an azimuthal gyrostabilized link 45which carries an index 46. vThis link may be clamped to the disc 43 toconnect the disc also to the azimuth stabilized member by means of theset screw 41.

Thereis vindicated on Fig. 4 a trianglevformed of sides a, b and c. Theside a of this triangle corresponds to that portion of the long .arml3|? of the bell crank lever 3| that lies between the center of thepivot 32 and the center of the pin 38,v side `IJ corresponds with thatportion of the link 28 which lies between the center of the shaft 24 andthe center of the pin 38, and side c corresponds with the link 29between its pivots lo- M cated at the centers of shafts 24 and 32. Inorder that the angle between links 28--29 (sides b and c) may be madeequal to the offset angle 00u of Fig. 1Y the triangle abc must besimilar to triangle PTA (abc') of Fig. 1.

The following conditions establish similarity of these two triangles:

a is parallel to a' (TA) 1 c is parallel toc (PA) 3 The above conditionsare Nfulfilled in the following manner:

Before the bombing mission the particular target (T) is selected as wellas the tracking or aiming point A. Accordingly, the true bearing of theaiming point from the target @M0 is known. The inner disc 42 is clampedby means of the knurled knob 49 to the outer disc 43 so that, as shownin Fig. 4 the reference mark 44 on the inner disc will be set at anindication on the inner graduations of the outer disc corresponding tothe angle 0m. As an inspection of Fig. 4 will reveal, this referencemark always points in a direction parallel to the long arm 36 of thevbell crank lever 3|. This is achieved because the inner disc and arm 35are attached so that the reference mark on the inner disc isperpendicular to the linkr35; furthermore, the link 35 is parallel tothe short arm of the bell crank 33 which is rigidly attached at an angleof 90 to the long arm 36. When the bombing plane is in iiight the innerand outer discs, now clamped together along with the links 29, 33, 34and 35, are positioned by the operator by movement of the targetselection knob I3, for example, so that the reference mark,50 on theframe 30 will be positioned opposite the calibration mark on the outerdisc which corresponds to the compass heading of the bombing aircraft.The zero calibration on the outer disc 43 will now point to the truenorth. The outer disc 43Y is now clutched to the link 45 by means of theset screw 41 so that the outer disc also becomes stabilized in azimuthabout the axis of shaft 24'. The zero mark on this disc will thenmaintain a true northerly bearing with respect to the aircraft. Thereference mark 44 on the inner disc 42 having previously been set atanangle equal to @M0 will correspond .to the true bearing of the aimingpoint from the target.

Since the arm 36 is parallel to vthe reference mark 44 of disc 42 thecondition (1), e. g., that the side a of the triangle of Fig. 5 isparallel to side a' of the triangle of Fig. 1,'is established.

Referring now to condition (2) above, .e. g., that the ratio of sidesa-c of the triangle of.Fig. 4 is equal to the ratio of sides a-c' of thetriangle of Fig. 1; as previously described the block 38 is adapted tobe driven by the worm gear 4| and is secured to the slide engaging thelink 28 by means of a pin 38. This worm shaft 4| is adapted foroperation to maintain the side a of the triangle abc of Fig. 4 atsuchrlength that condition (2) is fulfilled. Although this could be donemanually by rotating the worm shaft 4| with a suitable mechanicalconnection, means is provided for achieving this conditionautomatically. This means comprises the motor 5|-and its respectiveenergizing circuit. This motor 5| receives its energizing voltage fromthe output of the differential amplifier 52. This amplifier circuit issuchthat its output is proportional or otherwise functionally related tothe difference in magnitudeiof two voltage inputs VA and AVG,

Where AVG is the voltage drop obtained from the l potentiometer (Fig. 4)across the portion thereof between the ground end 54 and the slide wire55. The voltage VA supplied to the differential amplier is madeproportional to the offset ground range of the aiming point A, i. e., TAof triangle Since VA is proportional to TA it is also proportional toside a of the triangle abc' of Fig.

1. Inasmuch as this ground range of the aiming point from the target isknown prior to the bombing mission the proportionality factor K may bedetermined so that The voltage VG which also supplies thedifferentialamplifier is derived from the potentiometer 53 which is mechanicallyattached to the arm 36 of the bell crank lever 3|. Moreover the Slidewire 55 is mechanically attached to the mov-'- able block 38 so thatthe. point of contact of the slide wire 55 with the potentiometer 53will coincide with the center of the pin 38; and the effec-VA Thevoltage VG is derived -by circuit means illustrated and described in thecopending application of Havens and Lentz, S. N. 620,135, `led October3, 1945, iwhich circuit details are omitted here in the interest ofclarity. The voltage AVG is applied to the dierential amplifier byconnecting the slide wire 55 to its input terminal so I that the voltageAVGr is dependent upon the portion of the slide wire 55 relative to thelength L of the potentiometer. Inasmuch as the slide wire ismechanically coupled to the block 38 and moves with the block, thedistance AL corresponding to AVG will be equal to a of thetriangle.ab'c' oi" i Fig.4 4. This slide wire will be moved along the Y'potentiometer by the motor to a position of rest wherein Y .7.. At this1positlcn...AL lwill feqnal a .and since -VA is-eqnal'lto Ka' SinceMinis proportional to a and -Vo is .PI-0'- poiitional, to .c

AVG/V,G=a/c' 3 .And1 further since the voltage drop along thepotentiometer 'is uniform, this Voltage drop can bev expressed in termsof length of the potenti-- ometer thus:

but L i's made equal to c and AL is equal to a, accordingly:

.Condition r3.) above is fuinued by the act of pilotingA .the bombingaircraft P. This results fromz-the fact that the bombing aircraft. isheaded Y so .that the .aiming point as viewed on the: screen of the.-B-scope coincides with the azimuth cross hair, The fact that condition(3) is vthereby fulfilled .may be seen from the following.considerations (o) Because of the coincidence ofthe aiming point A withthe azimuth cross hair on the screen, the-aiming pointbearing mustcorrespond with the cross hair bearing.

`(b).r Sidec' 0f Fig. 1 lies in the direction kof the shaft 24 will thusposition the link ,29 so that.

it corresponds to the actual aiming point bearing at `a particularinstant. Since the action of the linkage of Fig. 4 is such that theposition of the link 26 and its shaft 24 Ydiffer in angular positionfrom link 29 and its corresponding shaft 24' byan angle equal to off.

The telescope I4 `has been included in the description of the drawing torepresent the optical portion of the bomb sight vand `is representativeofthe line of sight to the target. Since the telescope I4 is positionedby the shaft 24 to point at all times directly toward thetarget, thebombing run, although initiated by means of radar, may befcompletedoptically at any time there is-a break in the overcast or that thetarget is otherwise visible.

Itisfclear that various `vmodifications Yin -constr-uctionfandarrangements of partsmay be made without departure from the spirit andscope of the present vinvention `and the invention is not thereforelimited by the illustration of the specic .preferred example orotherwise thanby the appended 4set of claims.

I claim:

l. In .a bombing system for maintaining a collision course between amoving aircraft and a stationary target by tracking a stationary aiminglpoint, the combination of a member stabilized in azimuth 'about apredetermined axis, a lrst pantograph comprising a plurality of linkspi'voted at spaced companion points in parallelogram form, relativelyAadjustable means coupling said pantograph' to. said member .at Aone :ofAsaid and circuit means for energizing. said electrical drive means' tomaintain said arm at a length whereby the 'ratio :of the .length ofvsaid arm to the length Iof the said adjacent .link of said secondpantog-raph is-equalrt'o the :ratio of the dis.- tance of said aimingpoint from said target =to the distance of the tracking. lpointfromznsaid target.

2. A 'bombing system .for maintaining. acollision .course between amoving .aircraft and stationary target by tracking with .radarastationary aiming point having a known range and bearing fromsaidtarget, a rst'and'second shaft rotatable on saidaircraft andmanually -adjustable with respect thereto, an azimuth stabilized memberadjustably coupled to ysaid -first shaft, a radar antenna positioned in-azimuth'relative to said aircraft by said second shaft to a .mean axisof scan for tracking said aiming point, va linkage mechanism includingan azimuth -stabilizedmember having a reference mark for indicating thetrue heading of said aircraft interconnecting said first and secondshafts to alter the relative angular position thereof, means for settingsaid linkage .mechanism whereby the bearing of a link thereof relativeto said reference mark of said azimuth stabilized member equals the truebearing of said aiming Vpoint from said target, means adjusting saidvfirst shaft `relative to said member whereby the vdifference in angularposition of said shafts is equal y to the difference in bearing of saidltarget and tracking point from said aircraft, and means responsive tothe change in ground range of said aircraft from said tracking point foraltering'the angular position of said link relative to said member tomaintain the bearing of said link equal to the difference in bearing ofysaid target and tracking point whereby said mean axis of scan will bemaintained vin the direction of said tracking point and said aircraftwill follow a collision course toward said target.

.3. The combination dened in claim 1 above wherein said circuit meanscomprises a differential amplifier the :output of which .isa function.of the difference in magnitude of two voltage inputs, means forlapplying to said ramplifier a first voltage input proportional Yto theground y range from said target to said .tracking point,

a potentiometer mounted on said adjustable arm having va length equal tothe length of said. adjacent link -of said second pantograph and avoltage ldropthroughout said length proportional to the ground rangefrom said target to said tracking point, a contact for saidpotentiometer secured to the end of said arm at its pointof connectionwith said adjacent link of said flrst pantograph and movable with theend of said contact is positioned vto make the .length cit-said meansfor generating an angle equal to the dif- 10 ference in bearing fromsaid aircraft to said target and aiming point, and means for adding anangle equal to this difference in bearing to the 10 angle between theheading of said aircraft and line of sight for establishing a mean axisof scan for said antenna.

BYRON L. HAVENS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 2,414,108 Knowles Jan. 14, 19472,438,112 Darlington Mar. 23, 1948

